A Rapid Thermal Annealing (RTA) is a thermal handling process for a short time at a high temperature. Typically, a wafer is placed onto a quartz stand within a process cavity and heated using a light source with high intensity. In a manufacturing process of an advanced integrated circuit, the RTA has been widely applied to procedures of thermal activation of implanted impurities, formation of metal silicide, etc.
Integrated circuit manufacturing technologies generally fabricate repeatedly arranged plural chips on a wafer simultaneously. For a product with plural chips, thermal budgets for the chips may vary because their semiconductor structures differ for their respective application scenarios. Therefore, an improvement of uniformity of an RTA process has been a technical issue under study in the industry.
For example, both an active area and a gate in a radio frequency circuit chip are distributed at a low density, and an active area or a gate in an SRAM circuit chip is distributed at a large density. On the other hand, areas with different distribution densities of an active area or a gate may be present even in the same chip. Such a difference of distribution densities of semiconductor structures, e.g., an active area, a gate, etc., may result in a difference of local temperatures in a wafer subject to a rapid thermal annealing process, thereby influencing uniformity of the process.
There is disclosed in Chinese Patent Publication No. 101454870A a method for providing a uniform temperature in a defined area across a wafer during a rapid thermal annealing process, which includes determining a first reflective index in a first part of the defined area by measuring the density of a first structure in the first part. Next, the method determines a second reflective index in a second part of the defined area by measuring the density of a second structure in the first part. Specifically, the first structure includes a diffusive dummy shape and a poly-silicon conductive dummy shape (non-active pseudo structure), and the second structure includes an active circuit structure. Then, the first reflective index and the second reflective index are compared and balanced through adjusting the amount by which the diffusive dummy shape and the poly-silicon conductive dummy shape in the first structure overlap. However, this method is simply based upon the balance between the different areas in the wafer but is not linked with consistency of electrical performance of a semiconductor device throughout the wafer.
The phenomenon of temperature non-uniformity of a rapid thermal annealing process may influence directly the electrical performance of a semiconductor device in an integrated circuit, so that a parameter, e.g., a threshold voltage, a saturation current, etc., of the device in a local area may fail to reach a target value.